Plasma Cathelicidin is Independently Associated with Reduced Lung Function in COPD: Analysis of the Subpopulations and Intermediate Outcome Measures in COPD Study Cohort.

RATRIONALE: The antimicrobial peptide cathelicidin, also known in humans as LL-37, is a defensin secreted by immune and airway epithelial cells. Deficiencies in this peptide may contribute to adverse pulmonary outcomes in chronic obstructive pulmonary disease (COPD). OBJECTIVES: Using clinical and biological samples from the SubPopulations and InteRmediate Outcome Measures In COPD Study (SPIROMICS), we assessed the associations of plasma cathelicidin levels with cross-sectional and longitudinal COPD outcomes. METHODS: A total of 1609 SPIROMICS participants with COPD and available plasma samples were analyzed. Cathelicidin was modeled dichotomously (lowest quartile [< 50 ng/ml] versus highest 75% [≥ 50 ng/ml]) and continuously per 10 ng/ml. Fixed-effect multilevel regression analyses were used to assess associations between cathelicidin and cross-sectional as well as longitudinal lung function. The associations between cathelicidin and participant-reported retrospective and prospective COPD exacerbations were assessed via logistic regression. MEASUREMENTS AND MAIN RESULTS: Cathelicidin < 50 ng/ml (N=383) was associated with female sex, black race, and lower body mass index (BMI).At baseline,cathelicidin < 50 ng/ml was independently associated with 3.55% lower % predicted forced expiratory volume in 1 second (FEV)(95% confidence interval [CI] -6.22% to -0.88% predicted;=0.01), while every 10 ng/ml lower cathelicidin was independently associated with 0.65% lower % predicted FEV(95% CI -1.01% to -0.28% predicted;< 0.001). No independent associations with longitudinal lung function decline or participant-reported COPD exacerbations were observed. CONCLUSIONS: Reduced cathelicidin is associated with lower lung function at baseline. Plasma cathelicidin may potentially identify COPD patients at increased risk for more severe lung disease.